1. Field of the Invention
The present invention relates to a water-soluble coating composition applied on the surface of nuclear fuel rods to prevent scratching of the surface of the fuel rods, which are disposed in a nuclear fuel assembly for light water reactors. More particularly, the present invention relates to a water-soluble coating composition, which facilitates the formation and removal of a coating film and in which the resulting coating film may exhibit strength and durability equivalent to those of an existing lacquer coating film.
2. Description of the Related Art
In order to manufacture nuclear fuel assemblies for light water reactors, fuel rods are loaded into a skeleton. As such, the surface of the fuel rods is coated with lacquer to prevent or minimize scratching of the surface of the fuel rods and to enable efficient loading of the fuel rods. Currently, lacquer that is useful for coating nuclear fuel rods is nitrocellulose (NC) lacquer. This lacquer is a paint material that forms a protective coating film when the solvent evaporates therefrom, and enables the formation of a tough and rigid film despite having a quick drying rate. The coating film thus formed is dissolved again in a solvent for a de-lacquering process. The solvent used for the de-lacquering process is butyl acetate.
Nitrocellulose (NC), currently used as the lacquer material, is a derivative of a natural polymer, cellulose, and is in a white powder phase, but is difficult to handle because it has explosive combustion properties to the extent that it serves as the main component of gunpowder. Furthermore, nitrocellulose may be formed into a rigid film by the evaporation of a solvent, but such a film may become brittle. Hence, the addition of a plasticizer and an alkyd resin is required to form a coating film having proper hardness and flexibility. Moreover, such a film is used under the condition that it is dissolved in an organic solvent to ensure appropriate liquidity, which undesirably and inevitably causes environmental pollution problems due to the use of the organic solvent.
Hence, the need for the development of safe and harmless alternatives to lacquer has arisen, but organic solvent type lacquer is still used to date, owing to the absence of suitable alternatives.
In particular, a lacquering process for preventing scratching of the surface of nuclear fuel rods and a de-lacquering process for removing the lacquer coating after the fuel rods have been loaded, or processes similar thereto, cannot be found even in foreign companies such as Westinghouse or AREVA. Furthermore, techniques and inventive results for water-soluble coating compositions, including loading of fuel rods without a coating film or via spraying of water, are still lacking. Coating processes using organic solvents are general, and thus domestically ensured, but have a recent tendency to be replaced by safe water-based coating systems. Thorough research into water-soluble materials is ongoing, and overcoming the limitations of water is regarded as a critical factor influencing the success of the invention.